Historically, electrical connections between individual batteries in a battery pack were typically made with a commercially available nickel metallic strip. Nickel has been a common material for use as an electrical connection between individual batteries in a battery pack, due to multiple advantages. Advantages of the nickel strip include good corrosion resistance, resistance welding properties, and low electrical resistivity, good joinability by spot welding, and good solderability for terminal connections. Also, for the use of Lithium Ion batteries in low power “energy” sectors (e.g., personal computer notebooks, cell phones, tablets, digital cameras, etc.), the conductivity properties of pure Nickel have been sufficient to minimize detrimental heating of the battery pack.
However, as higher power applications have evolved (e.g., E-Bikes, Electric Vehicles, and Energy Storage), the need for a higher conductivity connection material has become apparent in order to minimize resistive heating which can degrade battery performance and safety. The need is particularly important in bus connections where electrical and thermal flow are concentrated into a smaller cross sectional area, and where numerous cells contribute to the cumulative heating effect in that cross sectional area. For example, the number of cells in an energy storage application may exceed 20,000 individual cells.
It is also desirable in the marketplace to develop a lower cost connection material with less sensitivity to the Nickel metal commodity market. Consequently, it is desirable to develop a material with a lower overall nickel content, while maintaining or exceeding the beneficial properties of electrical conductivity, thermal conductivity, weldability, solderability, strength, and formability.
The term “solderability” is defined as the ability of a metal substrate to be wetted by molten solder. Good resistance welding properties are characterized by the properties of the two systems to be welded together. It is advantageous to have systems with compatible thermal properties and melting characteristics, and for no deleterious or brittle metallic phases to form as a result of the welding of the two systems. “Electrical resistivity” (inverse of electrical conductivity) is a measure of the materials resistance to electrical current flow as a material property. It is readily converted to electrical resistance through consideration of the current carrying cross section.
The term “bond” includes the adhering or joining of metallic layers though a metallurgical bond. Techniques for forming this bond involve conventional processes, which include roll bonding (cold or hot), welding, explosion bonding, diffusion bonding, electrodepositing, adhesive bonding, and other techniques known by those with ordinary skill in the art.
Challenges exist in the roll bonding of laminate composites or systems with a soft copper sandwiched between two stronger alloys, particularly for higher thickness fractions of the soft copper. The primary issue is cyclical variation in the thickness of the stronger outside layers, leading to inconsistency in properties. Such challenges have limited the past introduction of a superior conductivity system for electrical connections between individual cells in a battery pack. To those skilled in the art, a system with a thicker copper layer, and higher electrical and thermal conductivities, is desirable. An example of a commercially pure nickel is UNS N02201 wrought metallic strip. UNS, which is short for “Unified Numbering System for Metals and Alloys,” is a systematic designation for metals. Due to highly unstable prices for elemental nickel, it is highly desirable to develop a low-nickel, multi-layer laminate with performance equivalent to conventional nickel systems.